A conventional fluid catalytic cracking system generally includes a fluid catalytic cracking (FCC) unit coupled to a catalyst injection system, a petroleum feed stock source an exhaust system, and a distillation system. The FCC unit includes a regenerator and a reactor. The reactor primarily houses the catalytic cracking reaction of the petroleum feed stock and delivers the cracked product in vapor form to the distillation system. Spent catalyst from the cracking reaction is transferred from the reactor to the regenerator to regenerate the catalyst by removing coke and other materials. The regenerated catalyst is then reintroduced into the reactor to continue the petroleum cracking process. The catalyst injection system maintains a continuous or semi-continuous addition of fresh catalyst to the inventory circulating between a regenerator and a reactor.
During the catalytic process, there is a dynamic balance of the total catalyst within the FCC unit. For example, catalyst is periodically added utilizing the catalyst injection system and some catalyst is lost in various ways such as through the distillation system, through the effluent exiting the regenerator, etc. If the amount of catalyst within the FCC unit diminishes over time, the performance and desired output of the FCC unit will diminish, and the FCC unit will become inoperable. Conversely, if the catalyst inventory in the FCC unit increases over time or becomes deactivated, the catalyst bed level within the regenerator reaches an upper operating limit and the deactivated or excess catalyst is withdrawn to prevent unacceptably high catalyst emissions into the flue gas stream, or other process upsets. Thus, the typical fluid catalytic cracking system also contains a withdrawal apparatus suitable for withdrawing materials from one or more units, like FCC units.
U.S. Pat. No. 7,431,894 teaches a catalyst withdrawal apparatus and method for regulating catalyst inventory in a fluid catalytic cracking catalyst (FCC) unit. In this design, a heat dissipater is located adjacent the metering device and is adapted to cool catalyst entering the pressure vessel.
U.S. Pat. No. 8,092,756 teaches a catalyst withdrawal apparatus and method for regulating catalyst inventory in a unit. One embodiment of this catalyst withdrawal apparatus includes a vessel coupled to a heat exchanger.
U.S. Pat. No. 8,146,414 teaches a method comprising withdrawing material from a FCC unit to a heat exchanger coupled to the fluid catalytic cracking unit. The heat exchanger has a material inlet; a material outlet; a cooling fluid inlet and a cooling fluid outlet with respective temperatures. The method further comprises measuring the respective temperatures at the material inlet, material outlet, cooling fluid inlet and cooling fluid outlet of the heat exchanger; determining a change in temperature between the material inlet and material outlet and determining a change in temperature between the cooling fluid inlet and cooling fluid outlet; and correlating the change in temperature between the material inlet and material outlet and the change in temperature between the cooling fluid inlet and cooling fluid outlet to a metric of material withdrawn from the unit.
The heat exchanger in U.S. Pat. No. 8,146,414 is disclosed to include a housing that includes a tube maintained at a spaced apart relation from a first conduit. The first conduit includes one or more protrusions, such as fins (studs or other geometric shape) extending into the coolant volume defined between the housing and the first conduit that increases the heat transfer area.
Although effective, the pipe-in-pipe heat exchangers described in the above inventions have several drawbacks, including that they are expensive to build, the coolant air blower is expensive to build and operate, and the thermal expansion of the piping as it heats and cools over these wide temperature extremes is problematic. The piping has to be designed so that the thermal stresses caused by expansion and contraction as the temperature cycles between hot (operating) and cold (not in operation) do not cause the pipe to fail. This requires long expansion bellows, and elaborate sliding piping supports, and exchanger supports that allow for movement.
Similar problems are encountered with such a heat exchanger design when extremely cold streams need to be warmed, for example cryogenic liquids that need to be brought to room temperature or above. In this case, the problem relates to piping contraction when in service, and expansion when the process is stopped. These problems are just the inverse of those stated above, and require very similar engineering design changes to accommodate them.
It is therefore desirable to attain an improved heat exchanger for cooling mixtures of particulate matter and gases from high temperature operations such as fluid catalytic cracking (“FCC”) process or warming material from cryogenic processes such as a pharmaceutical manufacturing process. We have discovered a new heat exchanger to cool mixtures of particulate matter and gases from industrial processes, and also to warm material from a cryogenic process.